This project is designed to study the developmental sequence of the monocyte-macrophage cell line. Beginning with the bone marrow stem cell, through the blood monocyte, and ending with the tissue macrophage, the surface display of Ia antigens, macrophage-specific antigens, and the functional capabilities of these cell corresponding to the expression of these antigens will be investigated. Extensive use will be made of quantitative immunofluorescence techniques to determine not only the presence or absence of a specific surface marker, but also the amount of surface antigen expressed by the cells during differentiation. Techniques permitting long-term in vitro cultures of these cells in a newly developed system which allows the use of flow cytometry to separate subsets of adherent cells will permit precise definition of the characterization of the developing cells, will allow us to assign different macrophage functions such as antigen processing and cytotoxicity to different types of macrophages, and will allow us to manipulate surface antigen expression and cell function of these subpopulations of cells in vitro. External factors altering the differentiation of these cells and affecting the modulation of surface antigens on these cells will be defined. Hybridoma technology will be applied for the further characterization of cell subsets. An extension of the project will investigate the relationship of the natural killer cell to the monocyte-macrophage cell line. Finally, the information gained in the study of normal differentiation will be applied to the study of neoplastically altered macrophages in man, and the characteristics of macrophages involved in various inflammatory pathological lesions.